Unhairing hides and skins



Patente Jan. 21, 194i STATES PATENT OFFICE nnnsmme HIDES AND sxmsJuliuslfannmuller, North Plainfield, N. J., and 'Hans Schleich, NewDorp, Staten Island, N. Y., assignors to 'Wallerstein Company, Inc., NewYork, N. Y., a corporation of New York No Drawing. A plication May 2,1939, Serial No. 271,322

1 1 Claims. (01. 149-2) in order to loosen the hair to such an extentthat.

it can be readily removed mechanically, whether by hand or machine.

One objection to this old process has always been that it was too slow.To meet this objection, it has been customary to add to the lime bathso-called sharpening agents such as sodium sulphide, the form of arsenicknown as red arsenic and various amines, such as methylamine. While suchsharpening agents speed up the loosening of the hair, their use isattended with disadvantages of their own. For example, it has been foundthat most of such sharpeners can be used only in limited amounts becausetoo large amounts result in damage to the skins or hides.

In fact, even with weak sulphide solutions there is danger of suchinjury if the bath treatment is prolonged. Moreover, the use of most ofthese Sharpeners often if not usually, results in damage to ordestruction of the hair. This latter point is of considerable importancebecause the hair, if it can be reclaimed, is or may be a valuableby-product.

As a solution to the dilemma above outlined,

present applicant Julius Pfannmuller has disclosed in a copendingapplication, Serial No.

87,328, a method of treating skins and hides which comprises adding tothe lime or other alkaline bath reducing sulphur-oxygen compounds, ofwhich sodium hydrosulphite is an ex- ,7 ample. With such a hath, notonly is the hairloosening operation accelerated, as compared to the oldlime bath treatment, but there is no dc to the hide or to the hair.Thus, notonly is time saved, but the leather, following hating, tanningand other subsequent operations,

is of superior quality and the hair. can be reclaimed as a by-product.

The sulphur-oxygen compounds in question,

and which are hereinafter considered in more detail, are referred to as"accelerators" for 'con-' venience and to distinguish them from thesocalled sharpeners above referred to.

In addition to the coarse long hair, which may' be termed the top hair,skins and hides have visible to the eye. If not eliminated, however,such fine hair shows clearly in the leather as soon as the. skins arefinished. As a result, such leather must be graded lower and, thoughsalable, it cannot bring the price of higher grade leathers. 6 The pricediiference between two grades of leather is usually large and there maybe a differential between the lowwt grade and the highest grade, in thesame kinds of skins, of several hundred perccent. 10

The fine hair can be eliminated by the use oi sulphides, such as sodiumsulphide, which burns off the hair and this procedure is followed in anumber of tanneries. But this burning off involves loss of the top hairwhich, as above stated, 15 may be a valuable by-product if it can bereclaimed, and also involves danger of damage to the skins.

In tanneries where the 'hair is not eliminated by burning ed, the finehair is usually removed 20 to a greater or less extent as an incident tothe, operations known as scudding" and .slating, subsequent to maindehairing. But such removal often causes considerable difllculty andoften results in leather requiring low grading. 25 For example, if thehair is not properly loosened, the. operator has to press down so muchon the skin he is apt to scufl or mechanically damage the same, e. g. bychipping out small areas on the grain. A piece of leather may be perfectexcept 30 for scuffed or' chipped spots or spots of unremoved hairs. Butit has to be low graded because it haspoor cutting value and shoemakers,for example, will accept as top grade only those skins which have goodcutting value. That 15,-35

skins which have bad spots will involve a certain loss in cuttingbecause such spots may prevent use of considerable areas. a

This problem of hair removal is of relatively little importance if theremoval is by hand, as in 0 that case the operator can give each skin acareful and more or less individual treatment. But such hand operationsare too costly for the majority' of tannery productions. With hairremoval by machinery, it is dimcult to obtain com- 45 plate removal ofvthe fine hair, and particularlya uniform removal, without sending ordamaging the grain of the skin, v As pointed o t in the eo-pendingapplication above mentioned, when both an accelerator, such 50 as sodiumhydrosulphlte, and a sharpener, such as sodium sulphide or red arsenicare added to the bath, the action of the sharpener is greatly enhanced.It follows that when such agents are conjointly used, the requisiteperiod for thorough quently reduced. Such a treatment also loosens thefine hair to such an' extent that its proper removal involves no greatdifliculty. Such accelerators, however, do not afford any substantialprotection to the hair from the attack of the sharpeners and there is,therefore, danger of damage to the hair. It has been found, for example,that when sodium sulphide ((66% Na s) in amounts above 0.1 percent,based on the soaked weight of hides or skins, is used in a lime or otheralkaline bath containing an accelerator, such as sodium hydrosulphite,the hair is attacked to a greater or lesser degree.

The difliculty of properly removing fine hair can be materiallylessened, at the same time avoiding the danger of damage to the hair andhide and obviating the necessity of expensive hand-beaming orhand-slating operations, by adding to the lime bath caustic alkali orsome substance or substances which will generate caustic alkali therein,for example, soda ash. In the co-pending application referred to, thereis disclosed the conjoint use of lime, an accelerator, such as sodiumhydrosulphite, and caustic'alkali. This solves the probe lem of removalof fine hair to a certain degree.

There is, however, still another problem involved.

If the amount of caustic alkali used is too small, it is still dimcultto remove the fine hair. On the other hand, if the amount of causticalkali used to obtain desired ease of removing finehair, it

may prove to be too greatan amountin another respect.

properly loosen hair but may so interfere with Su q e t ha ing, an i gor other operations that good grade leather cannot be obtained. i.

Returningto the question of too much caustic, when skins or hides aretreated in an alkaline bath r they become swollen and caustic alkaliswells out skins and hides much more than lime alone does. Before theskins can be tanned, they must be brought down or reduced." This isaccomplished by an operation known as hating or puering. Formerly,puering was applied.to a bath formed from dog manure and hating to apigeon manure bath or the use of artificial bates containing enzymaticpreparations. At present, however, the term "bating" ismore or lesscommonly used to cover all types of such-procedures. The

hating step is carried out both to render the skins,

leather, the permissible amount of caustic alkali issubjected to closelimitations. Thus, the amount of caustic alkali in the lime'bathnecessary to 'obtain thorough and proper "action on the fine hair maywell bein excess of the limit permissible in respect to the degree ofswelling.

It is an object of the present invention to provide a method of treatingskins and hides for the loosening of the hair such that thedisadvantages involved in the problems above set forth are avoided.

More particularly it is an object of the inven- 5 tion to provide ahair-l treatment such that all the hair, including flne hair, can beremoved properly and without undue difilculty and without resort to handremoval and, at the same time, such that there is no substantial damageor injury to hide or hair; such that excessive swelling ofthe skins orhides is avoided; and such that proper leather of good grade can besubsequently obtained.

We have discovered that when hides and'skins are subjected, for example,to the action of lime, sodium sulphide and sodium hydrosulphite underproper conditions and in a particular sequence, a new and unexpectedresult is obtained as compared to any of the procedures above outlinedand 20 more particularly as compared to the action of a bath containinglime, sulphide and hydrosulphitc simultaneously. By such treatment weattain a substantial improvement over the procedures above outlined. 25

In carrying out the invention, and citing the materials specified by wayof example, we first subject the hides or skins to the action of asodium sulphide solution in the absence of lime or other alkalinematerial. We then subject such hides 30 or'skins to the action of a limebath containing sodium hydresulphite.

- To this end, we first immerse the hides or skins in an aqueous bathcontaining sodium sulphide. In tannery practice, it is the usual customto wash and soak skins and hides prior to any treatmentwith chemicals.The sodium sulphide may be added to the soak water at anytime after ashort preliminary wash or the skins or hides may be subjected to thesulphide solution after the soaking 0 operation.

While the time of treatment in the sulphide bath may vary, treatments offrom one-half hour to twenty four hours have been found to givesatisfactory results. Generally speaking, the shorter the soaking periodprior to the sulphide treahnent the longer should the skins or hidesremain in the sulphidesolution. However, even with a long soaking, arelatively long sulphide treatment may be used.

The sulphide treatment may be conveniently,

, but not necessarily, carried out in the'paddle ordinarily used in theleather industry, the washed skins being placed therein and the sulphideadded to the water. The relative amount of water used 55 may vary but askin-to-water ratio of about 1 "to .4. based on-soaked or wet saltedskin weight,

has been found to give satisfactory results. For

dry skins, considerably more water will ordinarily be required. go

The bath temperature may be in what may be termed the normal range 1. e.from 55 to 70' l".

or somewhat higher. It is considered inadvisable to usetemperatureaabove F. In the event clan abnormal drop in room temperature during 05the process; it may be advisable to adjust the bath temperatures sincelower temperatures slow up the process. I

The relative amount of sodium sulphide used may vary. In thisconnection, we have discovered 70 that the available range depends, atleast in part, on the pH value of the sulphide solution and that therange canfbe widened by properly controlling such pH value.

Regardlms 01' pH value, the lean amount. 15

cated do not appear to effect any substantial sodium sulphide that issufflcient to obtain what are now considered practically effectiveresults, is

about /2 pound concentrated sodium sulphide (66% NazS) per 1000 poundsof skins or hides, figured on soaked weight. An amount between thatminimum up to about 5 pounds of such sodium sulphide per 1000 pounds ofskins or hides gives satisfactory results and within that range it isnormally unnecessary to pay any particular attention to the pH value. Ifhigher proportions are used, the hair is more or less attacked unlessthe pH value of the bath is properly adjusted. If, for any reason, it isdesired to use a higher proportion of sodium sulphide, the danger ofdamage to the hair can be avoided by adjusting the alkaline reaction ofthe solution to a pH value below 11.7. We have found that what are nowconsidered the best results are obtained if the pH value is adjusted toaround 10.6 or lower.

If adjustment of the pH value is indicated, this may be effected bymeans of any suitable agentv for reducing the alkalinity. Examples ofsuch agents are sulphuric, muriatic, boric or organic acids; sodiumbicarbonate or borate; or other acid salts or salts of a weak base suchas ammonium chloride; or organic amines.

If and when the pH value is thus adjusted, the relative amount of sodiumsulphide used may be safely increased up to 10 pounds per 1000 pounds ofskins or hides. Even a somewhatlarger proportion of sodium sulphide maybe used with- V out serious damage to the hair or skins but it is ourpresent belief that with amounts above the maximum mentioned there is nosuch increase in effectiveness as to warrant such increase inproportions.

After the sulphide treatment above described, I

tries, to designate such salts as hyposulphites.

In view, however, of the fact that the term hyposulphites has long beenused in this and other countries to designate salts of thiosulphuricacid (H2S2O3) more properly called thio-sulphates, we prefer to use theterm hyposulphites for salts 4 Of the acid H2S204.

Assuming that the skins or hides have been subjected to the sulphidetreatment in a paddle, the most convenient procedure is to replace thesulphide liquor with water and then mix in the lime and sodiumhydrosulphite. For this bath,

we have found it advisable to have the bath temperature aboveapproximately 60 F., say from 70 to 86 F.

The relative amount of lime used may vary within a considerable range.Ordinarily, amounts between about pounds and 250 pounds per 1000 poundsof skins or hides, based on soaked weight, give satisfactory results butoccasionally a somewhat higher proportionis desirable.

The relative amount of sodium hydrosulphite may also vary. We have foundthat from 4 pounds to -6 pounds per 1000 pounds of skins or hides(soaked weight) gives satisfactory results. Smaller proportions may beused but will be less eifective. Larger proportions may also be used butamounts materially greater than those indichange in the results, and,hence, are unnecessary.

While the duration of treatment in the limehydrosulphite bath may vary,we have found that a treatment of from 2 to 4 days, measured from thetime the lime is added, gives satisfactory resuits, the hair, includingfine hair, being in such a thoroughly loosened condition as to bereadily and properly removable by normal tannery procedure. Inthis-connection it should be noted that the hair will probably bethoroughly loosened in considerably less than 4 days. As previouslysuggested, however, the various operations involved .in the productionof leather are interrelated. Most tanneries consider that the durationof the lime or other alkaline treatment controls, to a considerableextent, the texture of the final leather. It follows that the durationof I treatment in the lime bath does not depend on the hair looseningfactor alone and a longer treatment than required for proper hairloosening may be desirable for other reasons. i I

Skins and hides treated according to the invention as so far describedwill have an alkaline swelling well below any degree of swelling that isconsidered excessive in the sense hereinabove referred to. In fact, inmany cases, there will not be as much swelling as tanners desire. Insuch case, the degree of swelling may be increased by, adding to thelime-hydrosulphite bath a caustic alkali. While the amount may vary, wehave found that from .05 percent to 5.0 percent, based on soaked or wetsalted skin weight gives satisfactory results, the proportion useddepending largely on the'degree of swelling desired. That is, the moreswelling desired, the greater the proportion of caustic used. Inreferring to the addition of a caustic alkali, it is to be understoodthat we include addition of caustic alkali as such or the addition ofany compound that will generate caustic alkali in the lime bath, forexample, soda ash or sodium sulphite.

Instead of using sodium sulphide in the first bath, other alkalinesulphides may be used.

Instead of using sodium hydrosulphite, other accelerators may be used.For the purposes of the present application, accelerators are to beunderstood to mean. reducing sulphur-oxygen; combinations, characterizedby being relatively stable in the dry state and having a substantiallygreater reducing power in solution than that of the sulphates,sulphites, sulphides or thio-sulphates. Such combinations includecompounds of the class of hydrosulphites and sulphoxylates, e. g.sodium, calcium, magnesium and zinc hydrosulphites and sulphoxylates,and corresponding organic compounds of sulphur and oxygen, such.

as the aldehyde] and ketone derivatives of the hydrosulphites andsuiphoxylates. Further examples are sodium, calcium,- or magnesiumformaldehyde sulphoxylate; zinc calcium hydrosulphite; sodium,calcium-magnesium or zinc formaldehyde -sulphoxylate or hydrosulphiteand other hydrosuiphites and sulphoxylatesof sodium,

I calcium, magnesium and zinc. In short, all sulphinicor disulphinicacid derivatives whether of inorganic or organic origin, aromatic oraliphatic, may be used.

, Instead of lime, or in conjunction with lime, other alkaline materialssuch, for example, as caustic soda or soda ash, may be used.

With the treatment described, the hair, including fine hair, -is sothoroughly loosened it can readily be removed by normal tanneryprocesses and without the necessity of recourse to removal by hand. Atthe same time there is no substantial damage or injury to the hair and,thus, the

1 alkaline swelling of the skins or hides.

It has been proposed in a United States patent to treat skins and hides,first in a sulphide solution of an alkalinity represented by a pHof 11.8to 12.2 and thereafter .to the action of a lime bath. It is stated insuch patent that the procedure referred to avoids damage or injury tohide or hair. Whether or not this is true, is a point not here involved.In any event, wehave found that with the procedure proposed in suchpatent the fine hair is often, if not usually, diflicult to remove.Moreover, we have found that with the pH values prescribed by thepatentee as critical and with the proportions of sulphides prescribed byhim, the hair is definitely attacked and damaged if, after the sulphidetreatment, the skins or hides are subjected to a bath such as we herepropose, namely, a. bath containing lime and an accelerator, such assodium hydrosulphite.

The following more detailed procedures are givenby way of example, suchprocedures having been found to give satisfactory results.

In each case the hair, including the fine hair, was readily removed. Ifany fine hair was left after the removal of the main hair, it wasremoved without difficulty as an incident to scudding. The top hair wasof good quality and could be reclaimed as a by-product. The leather,following hating, pickling, tanning, etc. was of excellent quality andgood grade.

Where the addition of chemicals is specified,

sufficient agitation to obtain a proper mix is to be understood. Limemeans hydrated lime throughout.

The sulphide solution was drained on and re- Example I 1000 poundscalfskins (salted weight) were washed in a drum for about 2 hours andthen.

hair fleshed. The skins were then transferred to a paddle containingsuflicient water to give a skin-to-water ratio of about 1:4. To thiswater had been added 3% pounds fused sodium sulphide (66% NazS). Theskins were paddled for 30 minutes and allowed to stand in the sulphidebath for After 20 hours, 2.5 pounds soda ash were added and the paddleturned a short time.

After a total of 3 days in the lime bath the skins were removed andunhaired on the usual unhairing machine. a

' Example II 1000 pounds calfskins were soaked overnight and put in apaddle having suflicient water to give a skin-to-water ratio of 1:4.5.Then there was added 4 pounds sodium bicarbonate and, after 10 minutes,6 pounds sodium sulphide (66% No.18) The skins were kept in this bathfor 17 hours. The pH of the soak liquor at end of soaking was placed bywater at. 80 F. Then there was added 100 pounds limeand, after 20minutes, 6 pounds sodium hydrosulphite. After 2 days i the lime 1 baththe skins were unhaired.

exam le 111 1000 pounds goatskins, dry weight, were soaked for one dayand put in a paddle containing about 7000 pounds water at about F. Thenthere was added, in the batches, a total of 8 pounds crystallized sodiumsulphide (33% Nags approx.) The skins were paddled for 1% hours. The pHshortly after the first addition was 8.7; after the second addition andat end of paddling, 9.3. The skins were kept in this bath over night.

Next morning the pH of the sulphide liquor was 8.5. The sulphide liquorwas drained off and replaced by water at F. There was. then added 300pounds lime and 3 pounds sodium hydrosulphite. After paddling for onehour and a rest period of 2 hours, there was added 12 pounds soda ashand 7 pounds more sodium hydrosulphite.

After 72 hours the liquor was drained oil. The skins were kept overnightin cold water and then.

, removed and dehaired.

Example IV water to give a skin-to-water ratio of 1:4.5. Then there wasadded 8 pounds sodium bicarbonate and, after 10 minutes 12 pounds sodium.sulphite (66%NaaS). The skins were left in this bath 3 hours, afterwhich'time the pH was found to be-10.0.

The sulphide solution was replaced by water at 80 F. To this'there wasadded 200 pounds lime, and, 'after 20 minutes, 12' pounds sodiumhydrosulphite. The skins were eft in this bath overnight. Next day therewas added 5 pounds soda ash. After a total of 3 days following additionof the lime the skins were removed and unhaired.

Example V 2000 pounds calfskins weresoaked for 16 hours and put in apaddle containing sufllcient water to give a. skin-to-water ratio of1:4.5. Then there was added 2.5 pounds sodium sulphide (66% N823) Theskins were left in this sulphide bath for 4 hours.

The sulphide solution was replaced by water at 78 F. To this wasadded200zp0unds lime and, after 20 minutes, 12 pounds sodium hydrosulphite;After 24 hours there was added 'lo pounds soda After remaining in thelime bath 3 days the skins were removed and .unhaired.

What is claimed is:

1. The method of loosening the hair of skins and hides which comprisessubjecting the-skins or hides to the action of an aqueous bath to whichhas been added an alkaline sulphide and which is substantially free ofany other alkaline material, and thereafter subjecting the skins orhides to the action of an aqueous bath to which has been added analkaline material and a material selected from the group consisting ofhydrosulphites, sulphoxylates and their aldehyde and ketone derivatives.

2. The method of loosening the hair of skins and hides whichcomprisessubjecting the skins or hides to the action of an aqueous bathto whichhas been added an alkaline sulphide and which is substantially free ofany other alkaline material, and thereafter subjecting the skins orhides to the action of an aqueous bath to which has been added lime andamaterial selected from the group consisting of hydrosulphites,sulphoxylates and their aldehyde and ketone derivatives.

3. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added an alkalinesulphide and which is substantially free ofany other alkaline material, and thereafter subjecting the skins orhides to the action of an aqueous bath to which has been added analkaline material and a hydrosulphite.

4. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added an alkaline sulphide and which is substantially free ofany other alkaline material, and thereafter subjecting the skins orhides to the action of an aqueous bath containing lime and ahydrosulphite.

5. The method of loosening the hair of skins and hides which comprisessubjecting the sk ns or hides to the action of an aqueous bath to whichhas been added sodium sulphide and which is substantially free of anyother alkaline material, and thereafter subjecting the skins or hides tothe action of an aqueous bath containing an alkaline material and sodiumhydrosulphite.

6. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added sodium sulphide and which is substantially free of anyother alkaline material, and thereafter subjecting the skins or hides tothe action of an aqueous bath containing lime and sodium hydrosulphite.

7. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added an alkaline sulphide and which is substantially free ofany other alkaline material, adjusting the alkaline reaction of the bathto a pH valuebelow 11.7, and thereafter subjecting the skins or hides tothe action of an aqueous bath to which has been added an alkalinematerial and a material selected from the group consisting ofhydrosulphites, sulphoxylates and their aldehyde and ketone derivatives.

8. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added an alkaline sulphide and which is substantially free ofany other alkaline material, adjusting the alkaline reaction of the bathto a pH value below 11.7, and thereafter subjecting the skins or hidesto the action of an aqueous bath to which has been added lime and amaterial selected from the group consisting of hydrosulphites,sulphoxylates and their aldehyde and ketone derivatives.

9. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added sodium sulphide (66% NazS) in an amount betweenapproximately /2 pound and approximately 5 pounds per 1000 pounds ofskins or hides, figured on soaked weight, and which is substantiallyfree of other alkaline material, and thereafter subjecting the skins orhides to the action of an aqueous bath to which has been added lime anda material selected from the group consisting of hydrosulphites,sulphoxylates and their aldehyde and ketone derivatives.

10. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added sodium sulphide (66% 118.28) in an amount betweenapproximately pound and approximately 5 pounds per 1000 pounds of skinsor hides, figured on soaked weight, and which is substantially free ofother alkaline material, and subjecting the skins or hides to the actionof an aqueous bath to which has been added lime and sodiumhydrosulphite. 1

11. The method of loosening the hair of skins and hides whichcomprises-subjecting the skins or hides to the action of an aqueous bathto which has been added sodiumsulphide (66% Nazs) in an amount in excessof approximately 5 pounds per 1000 pounds of skins or hides, fi red onsoaked weight, and which is substantially free of other alkalinematerial, adjusting-the alkaline reaction of the bath to a pH valuebelow 11.7, and thereafter subjecting the-skins or hides to the actionof an aqueous bath to which has been added an alkaline material and amaterial selected from the group consisting of hydrosulphites,suiphoxylates and their aldehyde and ketone derivatives.

12. The method of loosening the hail of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added'scdium-sulphide (66% Na s) in an amount in excess ofapproximately 5 pounds per 1000 pounds of skins or hides, figured onsoaked weight, and which is substantially free of otheralkalinematerial, adjusting the alkaline reaction of the bath to a pH valuebelow 11.7, and subjecting the skins or hides to the action of anaqueous bath to which has been added lime and sodium hydrosulphite.

13. The method of loosening the hair of skins and hides which comprisessubjecting the skinsor hides to the action of an aqueous bath to whichhas been added an alkaline sulphide and which is substantially free ofany other alkaline material, and thereafter subjecting the skins orhides to the action of an aqueous bath to which has been added lime andsodium hydrosulphite, the latter being added in an amount from about 4pounds to about 6 pounds per 1000 pounds of skins or hides, figured onsoaked weight.

14. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath to whichhas been added an alkaline sulphide and which is substantially free ofany other alkaline material, and thereafter subjecting the skins orhides to the action of an aqueous bath to which has been added lime anda material selected from the group consisting of hydrosulphites,sulphoxylates' and their aldehyde and ketone derivatives, said secondbath also containing a caustic alkali.

15. The method of loosening the hair of skins and hides which comprisessoaking the skins or hides in water, adding to the soak water m alkalinesulphide, leaving the skins or hides in such bath for from /2 to 24hours, replacing said bath with water, adding an alkaline material and amaterial selected from the group consisting of hydrosulphites,sulphorwlates and their aldehyde and ketone derivatives, and leaving theskins or hides in said second bath for from 2 to 4 days.

16. The method of loosening the hair of skins and hides which comprisessubjecting the skins or hides to the action of an aqueous bath, atnormal temperature, to which has been added an alkaline sulphide andwhich is substantially free of other alkaline material, and thereaftersubjecting the skins or hides to the action of a warm water bath towhich has been added an alkaline material and a material selected fromthe group consisting of hydrosulphites, sulphoiwlates and their aldehydeand ketone derivatives.

17. The method of loosening the hair of skins and hides which comprisessubjecting the skins, or hides to the action of an aqueous bath-to whichhas been added an alkaline sulphide and which.

5 is substantially free of any other alkaline material, thereaftersubjecting the skins or hides to the action of an aqueous bath to whichhas been added lime and sodium hydrosulphite, and controlling thedegreeot swelling of the skins or hides by adding to said second bathsuitable amounts of a. caustic alkali.

JULIUS PFANNMULLER. HANS SCHIEICH.

. CERTIFICATE OF CORRECTIOIL I Patent No. 2,229,125. January 21, 191 1.

lTULIUs PFANNHULLER, ET L.

It is herebj certified that error appears in the printed jepecificationof the above numbered patent requiring correction as follows: Page 3,first column, line 55,- for "hyposulphits read -"hydrosulphitee"--; and

I that the said Letters .Patent should be read with this correctiontherein that the same may conform to the record of' the case inthe Patent Office.

Signed and sealed this 18th day of February, A. 1). 19M.

Henry-Van A'rsdale, (Seal) Acting Commissioner ofPatents.

